Pore and Fracture Structure of Coal Reservoir Constrained by Coal Metamorphism

doi:10.19657/j.geoscience.1000-8527.2019.016

Abstract

Abstract:

To study the effects of coal metamorphism on the structure of pores and fractures, mercury intrusion porosimetry, low temperature nitrogen adsorption/desorption, vitrinite reflectance test, scanning electron microscopic (SEM) analysis, and fluorescence microscopy observation, were conducted to investigate the influence of coal metamorphic degree on porosity, Brunauer-Emmett-Teller (BET) specific surface area, Barrett-Joyner-Halenda (BJH) total pore volume and fracture structure and density. The results indicate that with increasing coal metamorphism, the coal porosity increases first and then decreases, and finally increases slightly. Micropore volume (<10 nm) shows a U-shaped change with the increase of vitrinite reflectance, and small pores show an inverted U-shaped trend. The BET specific surface area, BJH total pore volume, and fracture density (fracture type B, C, and D) of medium- to high-grade metamorphosed coal have the same U-shaped trend. However, for type B, C, and D facture density of medium- to high-grade metamorphosed coal, the minimum values occur near R_o,m=1.1%, and the fracture density reduction of type D fractures is highest when the fracture density decreases. Integrated with the results of vitrinite reflectance, the pore and fracture development are closely related to the four abrupt changes of the coal metamorphism.

Key words: coal, metamorphic degree, pore, microscopic fracture

CLC Number:

P618.11

FAN Qizhang, CAI Yidong, BEI Jinhan, WANG Weihao, ZHANG Xueying. Pore and Fracture Structure of Coal Reservoir Constrained by Coal Metamorphism[J]. Geoscience, 2020, 34(02): 273-280.

Figures/Tables 9

References 22

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样品	产地	R_o,m /%	中孔占比 /%	小孔占比 /%	微孔占比 /%	BET比表面积/ (m²/g)	BJH总孔体积/ (ml/g)
MRC1	大同	0.60	9.6	35.5	54.9	1.847	0.005 9
MRC2	谢桥	0.73	14.3	44.8	40.9	1.062	0.004 8
MRC3	大同	0.79	18.2	46.4	35.4	0.564	0.002 7
MRC4	大同	0.80	06.3	15.1	78.6	1.888	0.003 8
MRC5	淮南	0.81	20.1	66.2	13.7	0.601	0.003 8
MRC6	淮南	0.87	0	87.1	12.9	0.249	0.001 0
MRC7	平顶山	0.90	12.8	27.8	59.4	1.431	0.002 9
MRC8	淮南	0.94	37.5	58.1	4.4	0.223	0.001 4
MRC9	淮南	0.99	48.7	44.1	7.2	0.297	0.001 5
MRA1	沁水	1.70	32.0	61.0	7.0	0.241	0.001 0
MRA2	安鹤	1.70	47.3	52.7	0	0.115	0.001 1
MRA3	安鹤	1.90	24.4	67.2	8.4	0.394	0.002 9
HRC1	淮北	2.05	25.9	65.9	8.2	0.563	0.002 9
HRC2	沁水	2.20	0	93.8	6.3	0.189	0.000 5
HRC3	沁水	2.60	0	50.0	50.0	0.307	0.001 2
HRC4	焦作	2.90	63.1	28.1	8.8	0.339	0.001 6
HRB1	永夏	3.00	56.3	29.6	14.1	0.196	0.000 7
HRB2	沁水	3.20	0	100.0	0	2.145	0.000 3
HRB3	永夏	3.20	50.0	50.0	0	0.042	0.000 4
HRB4	焦作	3.70	6.7	35.3	58.0	4.697	0.007 4
HRA1	焦作	4.00	10.8	65.4	23.8	0.977	0.003 7
HRA2	焦作	4.10	24.4	75.6	0	0.271	0.000 8
HRA3	焦作	4.20	19.6	70.9	9.5	0.331	0.003 2
HRA4	荥巩	4.20	15.0	69.5	15.5	3.701	0.011 4
HRA5	荥巩	4.30	42.1	44.2	13.7	0.187	0.000 9

样品	产地	R_o,m /%	中孔占比 /%	小孔占比 /%	微孔占比 /%	BET比表面积/ (m²/g)	BJH总孔体积/ (ml/g)
MRC1	大同	0.60	9.6	35.5	54.9	1.847	0.005 9
MRC2	谢桥	0.73	14.3	44.8	40.9	1.062	0.004 8
MRC3	大同	0.79	18.2	46.4	35.4	0.564	0.002 7
MRC4	大同	0.80	06.3	15.1	78.6	1.888	0.003 8
MRC5	淮南	0.81	20.1	66.2	13.7	0.601	0.003 8
MRC6	淮南	0.87	0	87.1	12.9	0.249	0.001 0
MRC7	平顶山	0.90	12.8	27.8	59.4	1.431	0.002 9
MRC8	淮南	0.94	37.5	58.1	4.4	0.223	0.001 4
MRC9	淮南	0.99	48.7	44.1	7.2	0.297	0.001 5
MRA1	沁水	1.70	32.0	61.0	7.0	0.241	0.001 0
MRA2	安鹤	1.70	47.3	52.7	0	0.115	0.001 1
MRA3	安鹤	1.90	24.4	67.2	8.4	0.394	0.002 9
HRC1	淮北	2.05	25.9	65.9	8.2	0.563	0.002 9
HRC2	沁水	2.20	0	93.8	6.3	0.189	0.000 5
HRC3	沁水	2.60	0	50.0	50.0	0.307	0.001 2
HRC4	焦作	2.90	63.1	28.1	8.8	0.339	0.001 6
HRB1	永夏	3.00	56.3	29.6	14.1	0.196	0.000 7
HRB2	沁水	3.20	0	100.0	0	2.145	0.000 3
HRB3	永夏	3.20	50.0	50.0	0	0.042	0.000 4
HRB4	焦作	3.70	6.7	35.3	58.0	4.697	0.007 4
HRA1	焦作	4.00	10.8	65.4	23.8	0.977	0.003 7
HRA2	焦作	4.10	24.4	75.6	0	0.271	0.000 8
HRA3	焦作	4.20	19.6	70.9	9.5	0.331	0.003 2
HRA4	荥巩	4.20	15.0	69.5	15.5	3.701	0.011 4
HRA5	荥巩	4.30	42.1	44.2	13.7	0.187	0.000 9

裂隙类型	宽度 /μm	长度 /mm	形态
A型	≥5	≥10	较大的微裂隙,连续性好,延伸远
B型	≥5	<10	树枝状裂隙的树干部分
C型	<5	≥0.3	树枝状裂隙的树枝或树杈部分
D型	<5	<0.3	呈树枝状,方向性和连通性差

裂隙类型	宽度 /μm	长度 /mm	形态
A型	≥5	≥10	较大的微裂隙,连续性好,延伸远
B型	≥5	<10	树枝状裂隙的树干部分
C型	<5	≥0.3	树枝状裂隙的树枝或树杈部分
D型	<5	<0.3	呈树枝状,方向性和连通性差